Marie Venner contributed to this report.
Researchers using 1,200 years of soil dryness data from 1,586 tree ring studies say the western US, including California, Arizona, New Mexico, Oregon, and Idaho, are in the midst of the second most severe megadrought in the past 1200 years. A megadrought is defined as a severe drought that occurs across a broad region for a long duration, typically multiple decades.
According to The Washington Post, the research identified one other megadrought in the region that occurred in the late 1500s. The current drought began in 2000 and continues today. The difference, according to the researchers, is that today’s drought is being made more severe by human-caused global heating instead of naturally occurring changes in weather patterns. The study was published on April 17 in the journal Science.
“The megadrought era seems to be reemerging, but for a different reason than the [past] megadroughts,” Park Williams, the lead author of the study and a researcher at the Lamont-Doherty Earth Observatory at Columbia University, tells The Post. Even though there have been wet periods in the area covered by the study in recent years, “You can’t go anywhere in the West without having suffered drought on a millennial scale,” he says.
Benjamin Cook, a NASA climate scientist and co-author of the study, adds, “I think the important lesson that comes out of this is that climate change is not a future problem. Climate change is a problem today. The more we look, the more we find this event was worse because of climate change.” In 2015, Cook issued a warning that was eerily prescient. “Natural droughts like the 1930s Dust Bowl and the current drought in the Southwest have historically lasted maybe a decade or a little less,” he said. What these results are saying is we’re going to get a drought similar to those events, but it is probably going to last at least 30 to 35 years.”
Using an exhaustive review of tree rings dating back 1200 years, the researchers compared soil moisture with and without global warming-induced trends, “and we were able to determine that 30 to 50 percent of the current drought is attributable to climate change,” Cook says.
According to Jonathan Overpeck, a climate researcher at the University of Michigan who did not participate in the new study, the findings of this study are the first to link a megadrought that is already underway with anthropogenic climate change. “They are the first to show conclusively that we’re experiencing our nation’s first megadrought of the instrumental era,” he said in an email to The Post. “The real take home,” he added, “is that the Southwest is being baked by the burning of fossil fuels and other human activities, and the future implications are dire if we don’t stop climate change.”
Megadroughts In History
The scientific research indicates a megadrought occurred around 800 AD. Valerie Trouet, a researcher at the Laboratory of Tree-Ring Research at the University of Arizona, tells The Washington Post that event may have triggered the end of the Mayan civilization in North and South America and led to the Chichimeca War in Mexico, during which Native Americans and European settlers fought for decades, she says. “All of these past megadroughts have had severe impacts. We can expect there to be societal impacts now, too.”
Noah Diffenbaugh, a scientist at Stanford who studies the Southwest, points out that the drought the area is seeing today is happening when average global temperatures have increased only by a little over 1 degree Celsius. Many climate scientists predict temperatures could increase by 3 degrees Celsius or more by the end of this century. “The impacts we’ve already seen from one degree of warming really highlight the intensification of what’s coming,” Diffenbaugh says.
Snow Packs & Farming
What we are really talking about here are changes in the water cycle, the scientific model we all learned about in middle school. Sunshine evaporates water which collects into clouds and falls back to Earth as rain or snow. In the western part of the US, that snow has been piling up in the Rocky Mountains every winter for centuries and acting sort of like a water battery. As the seasons change, the sun’s warmth melts the snow, which replenishes the rivers and streams in the area until the following winter when the process begins all over again.
But the water cycle in the West is changing dramatically. Less snow is falling in the mountains and it is melting sooner, meaning later in the year there is no water available to keep those rivers and streams from drying up. Much of that water goes to grow crops in Arizona and the Central Valley in California. No water means no agriculture, with predictable results for farmers and the rest of America.
Researchers at Ohio State University have been studying what effect rising temperatures will have on snow melt. Yue Qin, assistant professor of geography and a core faculty of the Sustainability Institute at Ohio State, tells Science Daily, “In many areas of the world, agriculture depends on snowmelt runoff happening at certain times and at certain magnitudes. But climate change is going to cause less snow and early melting in some basins, which could have profound effects on food production.”
The Ohio State study was published April 20 in the journal Nature Climate Change. It finds that two areas that will be impacted the hardest by lower snow melt are the San Joaquin and Colorado river basins in the western United States. Other areas where agriculture will be particularly affected by changes in snow melt are located in southern Europe, western China, and Central Asia.
The problem is exacerbated by higher temperatures that prevent precipitation form falling as snow. Rain water is carried away immediately, often arriving before farmers need water for irrigation. Later in the growing season, there is no water left for crops. One possible solution would be to build more water reservoirs to capture the early spring rains for use later. Another strategy is to develop crops and agricultural methods that require less water. “We need to find ways to help those basins that will most need to adapt to the coming changes,” Qin says.
The unspoken concern here is that many of America’s fastest growing cities also depend on water from the mountains for sanitation, drinking water, and fire fighting. As the Earth continues to warm, the conflict between farmers and municipalities will continue to increase with potentially dire implications for global food production. The world may no longer fight wars over oil, but battles over access to fresh water could be next in many parts of the world, including the American West.